This invention relates to assays for ligands, e.g., antigens, in a liquid sample such as a body fluid. More particularly, the invention relates to a method and apparatus for the detection of a ligand in a body fluid such as urine using a conjugate comprising colored particles and a novel flow-through test cell.
Many types of ligand-receptor assays have been used to detect the presence of various substances, often generally called ligands, in body fluids such as urine. These assays involve antigen antibody reactions, synthetic conjugates comprising radioactive, enzymatic, fluorescent, or visually observable metal sol tags, and specially designed reactor chambers. In all these assays, there is a receptor, e.g., an antibody, which is specific for the selected ligand or antigen, and a means for detecting the presence, and often the amount, of the ligand-receptor reaction product. Most current tests are designed to make a quantitative determination, but in many circumstances all that is required is a positive/negative indication. Examples of such qualitative assays include blood typing and most types of urinalysis. For these tests, visually observable indicia such as the presence of agglutination or a color change are preferred.
Even the positive/negative assays must be very sensitive because of the often small concentration of the ligand of interest in the test fluid. False positives can also be troublesome, particularly with agglutination and other rapid detection methods such as dipstick and color change tests. Because of these problems, sandwich assays and other sensitive detection methods which use metal sols or other types of colored particles have been developed. These techniques have not solved all of the problems encountered in these rapid detection methods.
It is an object of this invention to provide a rapid, sensitive method for detecting ligands in body fluids. Another object is to provide an assay which has high sensitivity and fewer false positives than conventional assays. A further object is to provide a test cell for detection of low levels of ligands in body fluids. Another object is to provide an assay system which involves a minimal number of procedural steps, and yields reliable results even when used by untrained persons.
These and other objects and features of the invention will be apparent from the following description, drawings, and claims.